Abstract

1105

Growth factor receptor expression is a common aberration in cancer and both phosphatidylinositol 3’-kinase (PI3K) and AKT activity are induced by receptor activation. JNK can also be activated in response to PI3K to enhance cell survival and migration. To evaluate JNK as a potential therapeutic target in breast cancer we examined its role in normal mammary gland function and also in a transgenic polyoma virus middle T antigen (PyV MT) mouse mammary tumor model where the PyV MT transgene induces mammary tumors in a highly PI3K dependent fashion. We hypothesized that the loss of jnk1 or jnk 2 would inhibit tumor cell survival leading to delayed tumor development and also result in distinct defects in mammary gland development and involution. To assess the potential function of jnk 1 or jnk 2 in mammary gland development, wild type balb/c, jnk 1-/- and jnk 2-/- mice were sacrificed at virginity (>81 days), pregnancy day 15, 17, lactation day 9, and involution day 6. Mammary glands were studied using hematoxylin/eosin (H/E) stained glands and whole mounts at the various reproductive stages to compare the gland structure of the jnk 1-/- and jnk 2-/- mice to the wild type mice. To study the potential of jnk 1 or jnk 2 to influence mammary tumorigenesis, balb/C, jnk 1+/− or jnk 2 +/− mice were crossed with PyV MT FVB mice to obtain PyV MT transgenic female offspring that were either wild type or had heterozygous or homozygous deletions of jnk 1 or jnk 2. Mice were monitored daily and upon tumor detection, tumor latency was recorded. Tumor area was measured until tumors reached 1.5 - 2.0 cm2. Mice were then euthanized and representative mammary tumors from each genotypic group were either flash frozen, whole mounted or used to establish cell lines for later analysis. Cell line extracts and tumor protein lysates were immunoblotted for molecular markers and lungs were evaluated for metastases. We observed a combination of defects in mammary glands obtained from either jnk 1-/- or jnk 2-/- mice. H/E staining shows that jnk 2-/- virgin mammary glands have increased epithelial content with ductal disorganization. Comparison of jnk 1-/- or jnk 2-/- mammary gland whole mounts to wild type controls suggests that jnk knockout mice exhibit lactation defects and/or early involution. With regard to our mammary tumor model, we observed that jnk 1 or jnk 2 heterozygote mice experienced a significant increase in tumor latency. PyV MT mice experienced a median tumor latency of 68 days, while the median tumor latencies for PyV MT/jnk 1+/− and PyV MT/jnk 2+/− mice were 73 days (p= 0.01), and 99 days (p< 0.01), respectively. The PyV MT/jnk 1-/- and PyV MT/jnk 2-/- mice were 79 days (p< 0.01) and 71 days (p= 0.19), respectively. These data indicate that jnk 1 and jnk 2 play a complex role in tumor progression and in mammary gland function.